Various electro-optical systems have been developed for reading optical indicia, such as barcodes. A barcode is a coded pattern of graphical indicia comprised of a series of bars and spaces of varying widths, the bars and spaces having differing light reflecting characteristics. The pattern of the bars and spaces encode information. Barcodes may be one dimensional (e.g., UPC barcode) or two dimensional (e.g., DataMatrix barcode). Systems that read, that is, image and decode barcodes employing imaging camera systems are typically referred to as imaging-based readers or scanners.
Imaging-based readers may be portable or stationary. A portable reader is one that is adapted to be held in a user's hand and moved with respect to target indicia, such as a target barcode to be read, that is, imaged and decoded. Stationary readers are mounted in a fixed position, for example, relative to a point-of-sales counter. Target objects, e.g., a product package that includes a target barcode are presented or swiped past one or more transparent windows and thereby pass within a field-of-view of the stationary readers.
The imaging based readers typically comprise a sensor or photodetector that collects light reflected from the target indicia located on an article or target object. The sensor or photodector typically comprise charge coupled device (CCD) arrays, complementary metal oxide semiconductor (CMOS) arrays, or other imaging pixel arrays having a plurality of photosensitive elements or pixels.
Such photosensors electro-optically transform the graphic indicia into electrical signals, which are decoded into alphanumerical characters that are intended to be descriptive of the article or some characteristic thereof. A corresponding analog signal is generated by the photosensors that is decoded into a digital signal representative of the target indicia being read and is typically utilized as an input to a data processing system for various end-user applications such as point-of-sale processing, inventory control and the like.
In general, the photosensors discussed above require a source of illumination that is scattered across the target indicia within the photosensor's field-of-view (FOV) in order to produce the analog signal. A typical illumination system comprises light emitting diodes (LEDs), cold cathode florescent lamps (CCFLs), and the like that act as an illumination source for the imaging reader. The light reflected from the target indicia is focused through a system of one or more lenses of the imaging system onto the photosensors or sensor array. Thus, the target indicia within a FOV of the imaging lens system is focused on the photosensors or sensor array. Typically, for imaging 2D bar codes, two dimensional (2D) sensor arrays are utilized wherein a light receiving surface of the sensor array comprise multiple rows of light receiving photosensitive pixels.